Content: The Eye Topic: Co-ordination and Response Contents and instructions: This eBook contains Revision Notes, Questions and Answers. It is divided into 4 parts: Part 1 – Basic Structure and Function of the eye Part 2 – How we control the amount of light that enters the eye Part 3 – How we focus on near and far objects Part 4 – A revision game for you to print out and play Learning Objectives You need to be able to do:

1. Label and describe what each part of the eye does. 2. Know how the iris changes in bright and dim light 3. Know how the lens changes shape when it focuses on a near or distant object. 4. Be able to describe the changes in 2 and 3, with reference to a reflex arc.

If you are in Singapore use may want to use this links to view your syllabus. 2013 exam - http://www.seab.gov.sg/oLevel/2013Syllabus/5094_2013.pdf, page 15 2014 exam - http://www.seab.gov.sg/oLevel/2014Syllabus/5094_2014.pdf, page 15 © Chad Evans, www.knowneedlah.com , www.facebook.com/KnowNeedLah Disclaimer: This is an original work researched from various materials including those published by the GCSE and ‘O’ Level examining boards, the Qualifications and Curriculum Authority and the Departments for Education in England, Wales and Northern Ireland.

This eBook is written to be accessible and readily comprehensible. It may therefore use terms other than those used by the examining boards and other authorities. All information has been compiled in good faith by Chad Evans, but to the extent permitted by law, no warranty is given to its completeness or accuracy or whether it is up-to-date and Chad Evans may not be held responsible for any loss suffered as a result of the information or anyone acting upon its content. In the event that you are in doubt concerning your GCSE or ‘O’ Levels coursework or examinations we recommend that you seek further advice at your school or examining center.

Although all external links are checked at the time of compilation and on a regular basis, Chad Evans cannot be held responsible for the validity of any of these links. Chad Evans does not accept responsibility or otherwise endorse any information contained in the sites linked to from within these pages.

 

 

Part 1 – Basic Structure and Function of the eye

The eye is made up of the following parts. When shown a diagram without labels. You must be able to write down what each one is. You must also know the function of each part and preferably able to write it down too!

Cornea: This is transparent and curved, it bends the light rays towards the lens.

Iris: This is the coloured part of the eye. It contains muscle fibres that change the size of the iris. This in turn changes the size of the pupil, controlling the amount of light that enters the eye.

Lens: This focuses the light onto the retina.

Retina: This contains receptors, which detect light and sends electrical impulses towards the optic nerve. There are two types of receptors, cone cells detect colour and rod cells detect shades (black and white).

Optic nerve: This carries the electrical nerve impulses from the retina to the brain.

Blind Spot: This is where the optic nerve is joined to the retina, there are no receptors here, so it can not detect light and therefore images. This is why it is called the blind spot.

Fovea: Has the highest number of receptors (cones), providing the most detailed images for our sight.

Ciliary body/muscle: This changes the shape of the lens when the eye is focusing of near or distant objects.

Suspensory Ligaments: These attach the ciliary body/muscle to the lens. They slacken and tighten, depending on the movement of the ciliary body/muscle.

Vitreous Gel (Humour): Maintains the shape and structure of the eye

Retina

Vitreous�  Gel(humour)

Fovea

Cornea

Iris

Lens

Pupil {

OpticNerve

BlindSpot

CillaryBody

Suspensory�  Ligament

 

 

Example Questions (Long Answer - easy) 1) The diagram shows a cross section of an eye. Identify the parts A – K in the box below.

Letter Name of Part

A

B

C

D

E

F

G

H

I

J

K

 

 

Example Questions (Long Answer - easy) 2) The diagram shows a cross section of an eye. The table below state the function of parts A – K. Write the correct letter next to it function.

Function of Part Letter Carries impulses from the retina to the brain Transparent and curved, bends light towards the lens Contains receptors which respond to light by producing electrical nerve impulses

An area of the retina with the most receptors Changes the shape of the lens Focuses light onto the retina Attach the ciliary body to the lens, they slacken and tighten Muscle fibers which can change the size of the pupil An area of the retina with no receptors A transparent liquid that helps maintain the shape of the eye Surrounded by the iris, which changes the shape of the aperture, to regulate the amount of light entering the eye

 

 

Example Questions (Long Answer - moderate) 3) The diagram shows a cross section of an eye. In the table below state the function of parts A – K

Letter Function of Part

A

B

C

D

E

F

G

H

I

J

K

 

 

Example Questions (Long Answer - challenging) 4) The diagram shows a cross section of an eye. In the table below identify the parts of the eye and state their function, for parts A – K.

Letter Name of Part Function of Part

A

B

C

D

E

F

G

H

I

J

K

 

 

Answer Sheet: Part 1(Long answers) 1)

2) Function of Part Letter Carries impulses from the retina to the brain D Transparent and curved, bends light towards the lens H Contains receptors which respond to light by producing electrical nerve impulses

K

An area of the retina with the most receptors I Changes the shape of the lens B Focuses light onto the retina F Attach the ciliary body to the lens, they slacken and tighten A Muscle fibers which can change the size of the pupil G An area of the retina with no receptors C A transparent liquid that helps maintain the shape of the eye J Surrounded by the iris, which changes the shape of the aperture, to regulate the amount of light entering the eye

E

3) & 4) Letter Function of

Part Function of Part

A Suspensory Ligaments

Attach the ciliary body to the lens, they slacken and tighten

B Ciliary body/muscle

Changes the shape of the lens

C Blind Spot An area of the retina with no receptors D Optic Nerve Carries impulses from the retina to the brain E Pupil Surrounded by the iris, which changes the shape of

the aperture, to regulate the amount of light entering the eye

F Lens Focuses light onto the retina G Iris Muscle fibers which can change the size of the pupil H Cornea Transparent and curved, bends light towards the lens I Fovea An area of the retina with the most receptors J Vitreous

gel/humour A transparent liquid that helps maintain the shape of the eye

K Retina Contains receptors which respond to light by producing electrical nerve impulses

Letter Function of Part A Suspensory Ligaments B Ciliary body/muscle C Blind Spot D Optic Nerve E Pupil F Lens G Iris H Cornea I Fovea J Vitreous gel/humour K Retina

 

 

Part 2 – How we control the amount of light that enters the eye

The Iris consists of two types of muscle. These muscles contract or relax, which changes the size of the pupil. It is important to remember that it is the iris that controls the amount of light entering the eye, not the pupil. The pupil, is just a hole, it only appears black. Just like when you put a hole is a box, it appears black, but there is not actually anything there. The two types of muscle that the iris is made up of are circular muscle and radial muscle.

Dim Light Bright Light

Radial muscle contracts Radial muscles relax Circular muscles relax Circular muscle contracts Increased pupil size Decreased pupil size

It is sometimes hard to visualize. Try to think of the circular muscle working in the same way as your lips. When you contract the muscles in your lips, your mouth gets smaller, when they relax it gets bigger. Then think of the radial muscle being like your bicep, When it is relaxed it is long and thin, but when you contract your bicep, it becomes short and fat, which pulls your arm towards you. In the eye when the radial muscles contracts, it becomes short and thick, pulling the circular muscle towards itself, opening up the pupil. This is what happens when you relate it to a reflex arc. In Bright Light Increased light is detected by the retina (receptor). The retina sends electrical impulses along the optic nerve (sensory neurone) to the central nervous system (and brain). The brain sends impulses along a motor neurone to the circular muscle in the iris (the effector). The circular muscle contracts (radial muscle relaxes), the size of the pupil decreases. Reducing the amount of light that enters the eye. In the Dark Decreased light is detected by the retina (receptor). The retina sends electrical impulses along the optic nerve (sensory neurone) to the central nervous system (and brain). The brain sends impulses along a motor neurone to the radial muscle in the iris (the effector). The radial muscle contracts (circular muscle relaxes), the size of the pupil increases. Increasing the amount of light that enters the eye.

 

 

Example Questions (Multiple Choice)

1) Mark wakes up in a dark room and turns on the light (bright light). Which row in the table is the correct line to show the changes that take place in the iris? Diameter of the

Pupil Radial muscles of the iris

Circular muscles of the iris

A Increases Relax Contract B Decreases Relax Contract C Increases Contract Relax D Decreases Contract Relax 2) Mark plans to goes to sleep, when he turns off the light (bright light) and makes the room dark. Which row in the table is the correct line to show the changes that take place in the iris? Diameter of the

Pupil Radial muscles of the iris

Circular muscles of the iris

A Increases Relax Contract B Decreases Relax Contract C Increases Contract Relax D Decreases Contract Relax 3) The list below shows the events when a person turns on a light in a dark room, but in the incorrect order. In which order should the events occur? 1 the pupil diameter decreases 2 more light strikes the retina 3 nerve impulses are sent along the optic nerve 4 the circular muscles of the iris contract and the radial muscles relax A 1, 2, 3, 4 B 4, 3, 2, 1 C 2, 3, 4, 1 D 3, 2, 1, 4 4) The list below shows the events when a person turns off a light in a bright room, but in the incorrect order. In which order should the events occur? 1 nerve impulses are sent along the optic nerve 2 less light strikes the retina 3 the pupil diameter increases 4 the circular muscles of the iris relax and the radial muscles contract A 1, 2, 3, 4 B 4, 3, 2, 1 C 2, 1, 4, 3 D 3, 2, 1, 4

 

 

Example Questions (Long Answer – Challenging) 1) The diagram shows the cross section of an eye.

a) Which structure is mainly responsible for preventing light damaging the retina, by changing it shape in order change the amount of light entering the eye (provide letter and name)? ___________________________________ b) A person is sat on a train (light), the train then enters a tunnel (dark), before leaving the tunnel and returning back into sunlight (light) again. Explain the changes in the pupil with reference to your knowledge of the reflex arc. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________

 

 

Answer Sheet: Part 2 (Multiple Choice) 1) B 2) C 3) C 4) C Answer Sheet: Part 2 (Long answers) 1) a) Iris (G) b) On entering the tunnel decreased light is detected by the retina (receptor). The retina sends electrical impulses along the optic nerve (sensory neurone) to the central nervous system (and brain). The brain sends impulses along a motor neurone to the radial muscle in the iris (the effector). The radial muscle contracts (circular muscle relaxes), the size of the pupil increases. Increasing the amount of light that enters the eye. On leaving the tunnel increased light is detected by the retina (receptor). The retina sends electrical impulses along the optic nerve (sensory neurone) to the central nervous system (and brain). The brain sends impulses along a motor neurone to the circular muscle in the iris (the effector). The circular muscle contracts (radial muscle relaxes), the size of the pupil decreases. Reducing the amount of light that enters the eye. TIP Sometimes it helps to sketch out a diagram or the reflex arc before writing, so you don’t miss out any of the stages. The reflex Arc

Stimulus => Receptor => Sensory Neurone => Central Nervous System => Motor Neurone => Effector

 

 

Part 3 – How we focus on near and far objects

The lens shape is controlled by the ciliary body/muscle.

Focusing on a near object The ciliary body/ muscles contract. The Lens becomes thicker. The Light rays are bent much more towards the retina.

Focusing on a distant object The ciliary muscles relax. The Lens becomes thinner. The Light rays are not bent as much towards the retina.

 

 

Example Questions (Multiple Choice) 1) The cilliary body changes the shape of the lens in the eye. Which row in the table is the correct line when the eye is focused on a distant object? Shape of lens Cillary body A Slightly curved Contracted B Slightly curved Relaxed C Very curved Contracted D Very curved Relaxed 2) The cilliary body changes the shape of the lens in the eye. Which row in the table is the correct line when the eye is focused on a near object? Shape of lens Cillary body A Slightly curved Contracted B Slightly curved Relaxed C Very curved Contracted D Very curved Relaxed 3) Katie was watching a mosquito in her room. The graph below shows the changes in the curvature of the lens in the eye. At which point on the graph (A, B, C or D) was the mosquito closest (near object) to Katie.

 

 

4) Katie was watching a mosquito in her room. The graph below shows the changes in the curvature of the lens in the eye. At which point on the graph (A, B, C or D) was the mosquito furthest away (distant object) to Katie.

5) The diagram shows the cross section of an eye.

Which row in the table is the correct line to show which structures are receptors and which are effectors? Receptors Effectors A I and C B and G B I and K B and G C C and K A and E D F and I A and G

 

 

6) Susan is waiting for a bus. She sees the bus in the distance and then looks at her watch for 5 seconds, then back at the approaching bus. Which row shows the correct sequence to show the changes in the shape of the lens.

7) Susan late for her bus. She sees the bus pull away from the bus stop, just as she arrives. Which row shows the correct sequence to show the changes in the shape of the lens, as she watches the bus slowly move away from her.

 

 

Example Questions (Long Answer – Challenging) 1) The diagram shows the cross section of an eye.

a) Which structures is mainly responsible for changing the shape of the lens, to focus images onto the retina (provide letter and name)? ___________________________________ b) Katy is standing at the finishing line of the 100m track on sports day. She watches her friend run in the race. Explain the changes in eye, between when her friend stood at the start of the race and crossed the finishing line. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________

 

 

Answer Sheet: Part 3 (Multiple Choice) 1) B 2) C 3) D 4) C 5) B 6) C Answer Sheet: Part 3 (Long answers) 1) a) Ciliary body/muscles (B) b) When Katy is focused on her friend in the distance, the ciliary muscles relax. The Lens becomes thinner. The Light rays are not bent as much towards the retina. When Katy is focused on her friend at the finish line, the ciliary muscles contract. The Lens becomes thicker. The Light rays are bent much more towards the retina.

 

 

Part 4 – Revision Game (Biominos)

From the table below cut out “strips”, so they look like dominos (Biominos). DO NOT cut down the middle! Then shuffle the strips (as they are in the correct order, you may want to get someone to cut them for you, so you do not cheat). Starting from the “Biomino” with the word START, try to form a long line, until you reach the word FINISH. If you get stuck half way, you can always begin from the end and try to meet in the middle!

START

Chad Evans www.knowneelah.com

Iris

Controls the amount of light entering the eye In ‘Bright Light’

The circular muscle contracts and the radial muscles relax

Fovea

Has the largest number of cone cells In ‘the dark’

The circular muscles relax and the radial muscles contract

The Pupil

 

 

Not “a real thing”, merely an apature (hole)

Retina

Contains receptors that send electrical impulses along the optic nerve

When you focus on a

‘near object’

The lens is short and thick

Examples of receptors

in the eye

Fovea and Retina

When you focus on a

‘distant object’

The lens is long and thin

Vitrious Humour (Gel)

Maintains the shape of the eye

Examples of effectors in the eye

 

 

Cilliary body and iris Finish!

Good Luck in your Exams!